Apostolos Athanasiadis et al 96 Abstract: Conjoined twins have an estimated incidence of one in 50,000 to one in 100,000 births. The first cases of prenatal diagnosis of conjoined twins using B-mode ultrasound were reported in the 1970s, followed by prenatal real-time ultrasonographic diagnosis shortly thereafter. Since then, real-time ultrasound has been the most reliable method in establishing prenatal diagnosis of conjoined twins and in detecting associated anomalies. Moreover, recent improvements in real-time ultrasound technology — in some cases coupled with use of Magnetic Resonance Imaging (MRI) — have made early diagnosis of conjoined fetuses in the first trimester possible. Prenatal diagnosis of conjoined fetuses is considered essential for further management. Parents need detailed counseling in order to decide among various management options, which include the following: (a) pregnancy continuation and scheduled neonatal surgery, (b) termination of pregnancy, and (c) multifetal pregnancy reduction or selective fetocide in cases of high-order multifetal pregnancies with a component of conjoined fetuses. An interdisciplinary medical team, involving obstetricians, neonatologists, pediatric surgeons and anesthetists, should carefully approach and assist parents in their decisions. In special cases, additional consultation may be given by other specialists, even from specialized centers in other countries, depending on the area of conjunction, the involvement of other organ systems, and the presence of associated anomalies. Key words: Conjoined twins, conjoined triplets, prenatal diagnosis, magnetic resonance imaging, surgical separation, fetal echocardiography. INTRODUCTION Though an unusual phenomenon, conjoined fetuses have always drawn a disproportionately high degree of attention and interest from scientists and general public. This is apparently due to the intriguing processes involved in the pathogenesis of conjoined fetuses, the rare and even unique patterns of conjunction leading to complexity in management and surgical separation in individual cases, and a series of ethical questions coupled with a variety of emotional reactions and interactions between parents, relatives and health care providers. In recent years, the advent of real-time ultrasound and other novel imaging techniques have made early prenatal diagnosis of conjoined fetuses possible, enabling specialists and parents to decide Prenatal Diagnosis and Management of Conjoined Fetuses Apostolos Athanasiadis, Themistoklis Mikos, Menelaos Zafrakas Department of Obstetrics and Gynecology, Aristotle University of Thessaloniki, Greece. whether pregnancy should continue or not, and plan well in advance prenatal management, timing of delivery and immediate and long-term postnatal management, based on future quality of life and survival issues. HISTORICAL PERSPECTIVE Fetal conjunction usually involves two fetuses in a twin pregnancy. The term “Siamese twins” is often used for conjoined twins, since the most famous case of conjoined twins surviving to adulthood in modern times were born in Siam (today’s Thailand). This case was well known to the general public at their time, owing to numerous photographs published in newspapers around the world. Eng and Chang Bunker, were born in Thailand in 1811, grew up together, married two sisters, raised 21 children, and died both at the age of 69, a few hours apart from another, without ever being separated. 1 Long before this case and the invention of photography, in 1100 AD lived the Bidenden twins, who survived until the age of 34, probably representing the oldest well-documented case of conjoined twins surviving to adult life. 1 Until the invention of diagnostic imaging, starting with the use of diagnostic X-rays in the early 20th century, diagnosis of conjoined twins was possible only during labor. Labor arrest was the first sign in such cases, and sacrifice of one or both fetuses was often necessary in order to accomplish delivery. 2,3 The first report of prenatal diagnosis of conjoined twins using X-rays was published in 1934, while specific radiodiagnostic criteria were first described in 1950. 2,4,5 Even then however, prenatal diagnosis of conjoined twins could be missed, due to various possible factors: Absence of bone connections between twins, change of twins’ position in utero, and the fact that the investigator was usually not considering the possibility of conjoined twins. 2,6 The first cases of prenatal diagnosis of conjoined twins using B-mode ultrasound were reported in the 1970’s, followed by prenatal real-time ultrasonographic diagnosis shortly thereafter. 2,7-12 Since then, real-time ultrasound has been the most reliable method in establishing prenatal diagnosis of Donald School Journal of Ultrasound in Obstetrics and Gynecology, Jan-Mar 2007;1(1):96-104